The present invention relates to woven flame-resistant fabrics for apparel items.
Flame-resistant fabrics (also variously referred to as “fire-resistant”, “flame-retardant”, and “fire-retardant” fabrics) are fabrics that, once ignited, tend not to sustain a flame when the source of ignition is removed. A great deal of investigation and research has been directed toward the development and improvement of flame-resistant fabrics for use in various products such as bedding, clothing, and others. Flame-resistant clothing or apparel is often worn by workers involved in activities such as industrial manufacturing and processing, fire-fighting, electrical utility work, and other endeavors that entail a significant risk of being exposed to open flame and/or electrical arcs.
Flame-resistant fabrics include both fabrics that are treated to be flame-resistant as well as flame-resistant fabrics made from inherently flame-resistant fibers. The former types of fabrics are not themselves flame-resistant, but are made flame-resistant by applying to the fabric a chemical composition that renders the fabric resistant to flame. These types of fabrics are susceptible to losing their flame-resistance when laundered repeatedly because the flame-resistant composition tends to wash out or is rendered ineffective because of chemical reactions with laundering chemicals. In contrast, inherently flame-resistant fabrics do not suffer from this drawback because they are made from fibers that are themselves flame-resistant.
Various types of inherently flame-resistant (FR) fibers have been developed, including modacrylic fibers (e.g., PROTEX® modacrylic fibers from Kaneka Corporation of Osaka, Japan), aramid fibers (e.g., NOMEX® meta-aramid fibers and KEVLAR® para-aramid fibers, both from E. I. Du Pont de Nemours and Company of Wilmington, Del.), FR rayon fibers, oxidized polyacrylonitrile fibers, and others. It is common to blend one or more types of FR staple fibers with one or more other types of non-FR staple fibers to produce a fiber blend from which yarn is spun, the yarn then being knitted or woven into fabrics for various applications. In such a fiber blend, the FR fibers can render the blend flame-resistant even though some fibers in the blend may themselves be non-FR fibers, because when the FR fibers combust they release non-combustible gases that tend to displace oxygen and thereby extinguish any flame.
In the United States, it is desirable and often required for clothing worn by certain types of workers, such as petrochemical workers, to pass standard performance specification NFPA 2112-2012 (“Standard on Flame-Resistant Garments for Protection of Industrial Personnel Against Flash Fire”), Section 8.5 (Manikin Test), of the National Fire Protection Association. The NFPA standard is based on ASTM F1930, “Standard Test Method for Evaluation of Flame Resistant Clothing for Protection Against Fire Simulations Using an Instrumented Manikin.” This standard sets various standard performance specifications for a fabric, among which are specifications for the ability of the fabric to limit the extent and severity of burns to the human body when covered in single-layer garments constructed of the fabric. The NFPA 2112 Section 8.5 test covers quantitative measurements and subjective observations that characterize the performance of single-layer garments or protective clothing ensembles mounted on a stationary instrumented manikin. The conditioned test specimen is placed on the instrumented manikin at ambient atmospheric conditions and exposed to a propane-air diffusion flame with controlled heat flux, flame distribution and duration. The average exposure heat flux is 84 kW/m2 (2 cal/s/cm2) with durations up to 20 seconds. The test procedure, data acquisition, calculation of results and preparation of parts of the test report are performed with computer hardware and software programs. Thermal energy transferred through and from the test specimen during and after the exposure is measured by thermal energy sensors. The sensors are located at the surface of the manikin. They are used to measure the thermal energy absorbed as a function of time over a preset time interval. A computer-based data acquisition system is used to store the time-varying output from the sensors. Computer software uses the stored data to calculate the heat flux and its variation with time at the surface of each sensor. The calculated heat flux and its variation with time at the surface is used to calculate the temperature within human skin and subcutaneous layers (adipose) as a function of time. The temperature history within the skin and subcutaneous layers (adipose) is used to predict the onset and severity of human skin burn injury. The computer software calculates the predicted second-degree and predicted third-degree burn injury and the total predicted burn injury resulting from the exposure. The overall percentage of predicted second-degree, predicted third-degree and predicted total burn injury is calculated by dividing the total number of sensors indicating each of these conditions by the total number of sensors on the manikin. Alternately, the overall percentages are calculated using sensor area-weighted techniques, in the case of facilities with non-uniform sensor coverage. A reporting is also made of the above conditions where the areas that are uncovered by the test specimen are excluded. This test method does not include the approximately 12% of body surface area represented by the unsensored manikin feet and hands. No corrections are applied for their exclusion. The performance of the test specimen is indicated by the calculated burn injury area and subjective observations of material response to the test exposure.
In the United States, it is desirable and often required for clothing worn by certain types of workers to pass standard performance specification F1506 of the American Society for Testing and Materials (ASTM). This standard, entitled “Standard Performance Specification for Flame Resistant Textiles Materials for Wearing Apparel for Use by Electrical Workers Exposed to Momentary Electrical Arc and Related Thermal Hazards”, sets various standard performance specifications for a fabric, among which are specifications for the ability of the fabric to self-extinguish after being ignited. When the ignition source is removed, the fabric must self-extinguish in less than 2 seconds and have less than a 6-inch char length according to ASTM Test Method D6413 (“Standard Test Method for Flame Resistance of Textiles”, also referred to as the Vertical Flame test).
The F1506 performance standard also includes standard test ASTM 1959 (“Standard Test Method for Determining the Arc Thermal Performance Value of Materials for Clothing”), which measures the level of protection that the fabric provides against electrical arc exposure. This test method measures the arc rating of materials that meet the flame-resistance requirements of less than 150 mm (6 inches) char length and less than 2 seconds afterflame when tested in accordance with ASTM D6413. The method determines the heat transport response through the fabric when exposed to heat energy from an electric arc. This heat transfer response is assessed versus the Stoll curve, which is an approximate human tissue tolerance predictive model that projects the onset of a second-degree burn injury. During the procedure, the amount of heat energy transferred by the tested material is measured, using copper slug calorimeters, during and after exposure to the electric arc. The arc rating (denoted the “ATPV”) for the material is the amount of energy that predicts a 50% probability of second-degree burn as determined by the Stoll curve, or that causes the fabric to break open, whichever occurs first.
In addition to the above-noted performance specifications of fabrics, other properties are also important if a fabric is to be practical and commercially viable, particularly for clothing. For instance, the fabric should be durable under repeated industrial launderings and should have good abrasion-resistance. Furthermore, the fabric should be readily dyeable to dark, solid shades of color, and should be comfortable to wear. The fabric should have good dimensional stability and resistance to seam slippage.
As noted above, there are various fabrics that purport to provide some degree of flame-resistance. However, the prior art known to the applicant does not disclose or suggest the specific fabric of the present invention, which has been found to possess distinct advantages and characteristics, including passage of the NFPA 2112 Section 8.5 Manikin Test. The fabric is also comfortable to wear, is abrasion-resistant, and is durable under repeated industrial launderings.